ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

2pPP9. Contralateral stimulation and the masking overshoot effect.

Christopher W. Turner

Rebecca Waite

Karolyn Cummings

Melanie Rosen

Syracuse Univ., Program in Commun. Sci. and Disord. and Inst. for Sensory
Res., 805 South Crouse Ave., Syracuse, NY 13244

Overshoot is the increase in masked threshold for a short signal presented
at the onset of a masker compared to the threshold for a signal presented in
the temporal center of the masker. One hypothesis to explain this effect is the
slow onset time for masker-stimulated ipsilateral efferent activity to
influence the response to the masked signal. Recent physiological experiments
have shown that noise presented to the contralateral ear, which provides an
increment in efferent activity, can increase the neural detectability of short
tones masked by noise [Kawase et al., J. Neurophys. 70, 2533--2549 (1993)]. The
present behavioral experiment took advantage of these findings and measured the
amount of overshoot under conditions where a brief contralateral noise was
presented prior to the masker onset, in an attempt to ``prime'' the efferent
system prior to the masker onset. All measurements were conducted using insert
earphones, which provide approximately 80 dB of interaural attenuation. The
preceding contralateral noise reduced or eliminated the overshoot across a wide
range of masker levels. Possible mechanisms for the overshoot effect will be
discussed. [Work supported by NIDCD.]